1. Field of the Invention
This invention relates to a crank in a pushbutton tuner, and more particularly to a structure of a crank mechanism comprising side plates and a crank gear to be fixed on the side plates.
2. Description of the Prior Art
A pushbutton tuner is generally arranged to perform the tuning operation when rotating a crank to a predetermined extent by pushing a pushbutton and thereby inserting a tuning core interlocking the crank in a coil. Further, in such pushbutton tuner there is provided a manually tuning dial in addition to the above described tuning assembly by means of the pushbutton. When the dial is rotated, the crank is also rotated to a desired extent thus to tune the receiver at a station other than that selected by the pushbutton and to perform fine adjustment during the tuning operation. In this case, if the crank is kept connected to the tuning dial even upon operating the pushbutton, load becomes so large to disturb a smooth operation of the pushbutton. In this connection, there has been provided a clutch assembly between the crank and the tuning dial for releasing their engagement, thus reducing the load.
A pushbutton tuner of such type as shown in FIGS. 1 and 2 has been conventionally known. Side plates 3 and 4 are fixed at both sides of an upper and lower crank bars 1 and 2 by caulking and brazing manner. The side plates are formed with shafts 5 and 6 protruding thereon for allowing the crank to be supported on a frame of the tuner as well as crank pins 7 and 8 inwardly turning at the upper ends thereof for engaging a member for mounting a core of the tuner on. A crank gear 9 for transmitting rotational force between the crank and the clutch assembly is secured on the outer surface of the side plate 3. On the outer surface of the crank gear 9 there is rotatably mounted a gear 10 for preventing backlash between the crank gear 9 and a clutch gear of the clutch assembly.
In such conventional crank, there has been adopted the following means in order to fix the crank gear 9 with respect to the side plate 3. That is, the shaft 5 is inserted in a shaft bore at the center of the crank gear 9 to be held between a flange 5a formed on the shaft 5 and the side plate 3. Consequently the side plate 3 and the shaft 5 are secured to each other by caulking manner. With this arrangement, the crank gear 9 is still permitted to rotate about the shaft bore (shaft 5). Therefore, there has been proposed to provide associated through bores in portions other than the center shaft bores of the side plate 3 and the crank gear 9 for inserting a pin 11 therein and to caulk the pin 11, thus fixing the crank gear 9 with respect to the side plate 3 at two portions namely the shaft 5 and the pin 11.
However, since such fixing manner requires the pin 11 which is an independent member, it has had a drawback of increasing the number of parts as well as the weight of the crank. Further, when caulking the pin 11, the deformed head of the pin 11 protrudes on the surface of the crank gear 9. Therefore, in order to prevent the protruding portion from contacting with the backlash preventing gear 10, the pin 11 has to be mounted in a portion radially outward of the gear 10. In this connection, the side plate 3 and the crank gear 9 have to be so formed as to largely radially extend as shown in FIG. 2, resulting in requiring a large space for mounting the parts in. Further, the conventional fixing manner has been disadvantageous as requiring more manhour because caulking has to be done not only on the shaft 5 but also on the pin 11.